Significance Recent studies have begun to define the cognitive and neuropathological consequences of normal aging in the nonhuman primate. This research project has extend these findings by providing a detailed assessment of individual differences in memory function in a large population of aged rhesus monkeys (Macaca mulatta). Objectives The principal objective of the proposed project is to evaluate the hypothesis that memory is significantly compromised in only a subpopulation of aged monkeys. These investigations represent an essential component of an ongoing multidisciplinary program of studies aimed at 1) defining the neuropathological changes in the aged brian that are responsible for senescent cognitive discipline, and 2) evaluating the potential association between cognitive decline and other aspects of aging such as menopause. Results A spatial maze task for nonhuman primates has been developed specifically for this research program. Initial results have demonstrated a strong correspondence between the primate and rat model in assessing the effects of aging on spatial memory. In regards to the second major focus of this project we are extending our studies of hormonal levels and cognitive function to evaluate additional behavioral tasks in peri/post menopausal females as well as explore the effects of hormone replacement therapy. Future Directions Evaluation of cognitive function in the aged macaque population will continue with further evaluation of other parameters in the aging process. Specifically we hope to examine the effects on hormone replacement therapy on cognitive function.